I. Field of the Invention
The present invention is with respect to a process for making head pieces for containers with a membrane of laminate having a metallic barrier layer, the head piece being made up of a thermoplastic material and being made in one piece, and the head piece has a mouth-piece neck, a cone-like breast part next to it, a ring-shoulder next to the breast part and a round plate and a membrane of a laminate with a metallic barrier layer, the round plate being made beforehand and then joined with the head piece. Such a process is given in the German Auslegeschrift specification No. 1,486,193.
II. The Prior Art
In the case of this earlier process an inner part, having a membrane, is placed in the head on the inner side or melted for joining with its plastics material. The head and the inner part are in each case made beforehand. Such inner parts with a barrier layer are used more specially in the case of collapsible tubes and have the purpose of making the laminate tubes, having a barrier layer, more impermeable to gas in the head part. This purpose has in fact to a great degree been effected by the invention of the German specification No. 1,486,193, but however, because the inner part is placed inside the head piece, between the tube structure and the inner part there is a space generally equal in size to the thickness of the head piece and which is without any barrier layer and for this reason--being made of plastics only--is permeable to gas.
Further it is necessary, in this past process, to have the inner wall face of the head piece of truly the same form as the inner part, because otherwise, on putting in position, there would be no completely fluid-tight connection, or the head piece would have to be melted to a greater degree, something which would made the process of making more complex and longer. Because of the separate process for making the head piece and then separately joining up with the inner part, the process is made generally complex. Furthermore, the membrane is at the lower end of the neck, something making for an unpleasing form of the structure seen on opening the tube, and because of the depth of the neck it is harder for the layer to be broken open when the tube is to be used.
In the German Offenlegungsschrift specification No. 2,628,014 details are given of a process for making a packaging tube, in which a separately made head piece of plastics has placed on it a connection body in the form of a many-layer round plate made up of a metal layer bedded in plastics layers is placed so as to be on the cone-like breast part and to some degree on the ring-shoulder, and the two parts are welded togerther by a high frequency field. In this respect, a nearly completely gas-tight join is produced between the tube body with a barrier layer and the round plate. In this respect however, as well, the head piece and the round plate are separately produced and then joined together, so that the shortcomings noted come into play in this case as well. Furthermore in this past design a gas-tight membrane may only be made in a separate working step, this making necessary separate apparatus.
In this connection there has been a suggestion (see "Modern Packaging", June 1978, pages 27-29) for using a three-layer inner part, made up of aluminum foil, in a stopper cap, the foil having on one side a wax layer and on the other side a plastics layer. The wax layer is placed facing the end of the cap. The cap is screwed on to the head piece and then so placed in a high frequency field that the plastics layer of the inner part is joined with the plastics of the head piece by melting or welding.
In the German Auslegeschrift specification No. 1,786,574, an account is given to a process for making a laminate container with a barrier layer within the laminate. In this process the container tube body is run into a two-piece head piece casting mold, into which a round plate with a barrier layer is so placed that on injection molding of the head, taking place as the next working step, using a thermoplastic material at least the face, turned towards the inside of the container, is joined with the thermoplastic material or covered with it. In this respect the mouth piece neck is shut off by the plastics. Such a closure is not gas-tight and a knife is needed for opening it, this limiting use because of danger of injury, specially in the case of children. Although the radial distance of the outer edge of the round plate from the edge, to be joined with the head piece, is to be small, there is at the shoulder still a part made of plastics which, for this reason, is not gas-tight.
The Swiss Pat. Nos. 354,577 and 431,923 give an account of a process and an apparatus for making tubes, in which a tube body of thermoplastic material is placed on a rod and run into a head female mold, into which, beforehand, a measured out amount of thermoplastic material has been placed for producing the head piece, and then pressed, that is to say the head piece is injection molded onto the tube body. The apparatus has a turning table with a number of working stations, a ready-made membrane being placed in one station on the outlet opening of the head piece. The tubes so produced are in no way gas-tight.